1. Field of the Invention
The present invention relates to a castor and, more particularly, to a castor having a double-braking function so that the castor will stop rotating when being braked.
2. Description of the Related Art
A conventional castor 2 in accordance with the prior art shown in FIG. 6 was disclosed in the Taiwanese Patent Publication No. 528016. In the conventional castor 2, a drive member 23 is pressed downward to pivot a pivot portion 231 which has a press portion 232 which pushes a chamfered portion 241 of a slide 24 and compress an elastic member 27 so that a fixing pin 25 is movable in an elongate slot 201 of a castor body 20 to extend into one of a locking grooves 211 of each of two rollers 21 so as to lock and brake the rollers 21. At the same time, a locking block 26 is pushed by a second elastic member 28 to extend into a positioning recess 222 of an annular protrusion 221 of an upright support post 22 so that the castor body 20 is locked on and cannot be rotated relative to the support post 22. Thus, the castor 2 will stop rotating when being braked so as to provide a double-braking effect.
Another conventional castor 3 in accordance with the prior art shown in FIG. 7 was disclosed in the Taiwanese Patent Publication No. 255795. In the conventional castor 3, a drive member 30 is pressed downward and is pivoted about a castor body 32 to move its push end 301 which pushes a push block 31 to move downward in a receiving recess 32 of the castor body 32. At this time, the push face 311 of the push block 31 pushes a ramp 331 of a slide 33 so that the slide 33 compresses a spring 34, and a fixing pin 332 on an end portion of the slide 33 is moved and locked in one of a locking grooves 41 of each of two rollers 4 so as to lock and brake the rollers 4. At the same time, a ball 36 located at the bottom of a receiving hole 35 of the castor body 32 is pressed by a protrusion 333 of the slide 33 to move upward to compress a second spring 37 in the receiving hole 35, so that an enlarged flange 381 of a stop rod 38 is pushed upward by the second spring 37 to compress a third spring 37a. Thus, the stop rod 38 is pushed upward and is locked in a positioning hole 392 of a fixing block 391 of an upright support post 39 so that the castor body 32 is locked on and cannot be rotated relative to the support post 39. Thus, the castor 3 will stop rotating when being braked so as to provide a double-braking effect.